SUMMARY OF OBJECTIVES: To continue mortality follow-up of a previously studied cohort of approximately 40,000 Navy Korean war veterans, half of whom had potential for high exposure to microwave (radar) radiation during wartime service in the 1950's while the other half had little opportunity for such exposure. This cohort was previously followed from 1950 to 1974 by the Medical Follow-Up Agency of the National Academy of Sciences. In the current project, an additional 17 years of mortality data will be collected, and exposure assessment data will be augmented. Specific objectives are: 1) To assess mortality from all causes and from specific causes such as leukemia and brain cancer over the period from 1974 to 1991 in the exposed and unexposed subcohorts, each consisting of approximately 20,000 Navy veterans. Mortality in the high exposure group will be compared with that in the low exposure group; the cohort rates will also be compared to general U.S. population rates. Follow-up efforts will utilize Veterans Administration records (e.g., the Beneficiary Identification and Records Locator Subsystem (BIRLS) and the Veterans Administration Master Index (VAMI)), as well as Social Security Administration records and the National Death Index. 2) For a subset of high-exposure subjects exposure data will be abstracted from wartime service records, in order to evaluate whether the estimated intensity of exposure to microwaves is related to specific cancer deaths. Navy service records will be abstracted to obtain exposure estimates for all newly decreased men from the high exposure group, and for a random 10% sample of highly exposed cohort members.